Simulated Gravity with Centripetal Force
(and a lack of centripetal force)
We tend to feel like weight (the force of gravity) is acting on us only when we can feel the floor pushing back up on the bottom of our feet. That's why when we are in free fall we feel like we are weightless because nothing is pushing on the bottom of our feet. It also explains why when you are in an elevator and it accelerates downward, you feel like you weigh less than normal because the floor doesn't push as hard against your feet. (There are other factors that go into feeling weightless that have to do with your body not having to apply a force on your guts to keep them in place...but that has to do with feeling weightless not with simulating gravity.)
As we look toward the possibility of living in space for long periods of time (whether traveling or just staying in orbit around the Earth) we find that humans don't function as well in weightless situations. We get upset stomachs and in general we need a floor to push against us so we can move around an be productive. The question then arises, how do we create artificial gravity, or how do we simulate it?
- Velcro on the floor and on your shoes will stick you to the ground but you only feel the force when you try to move. It doesn't pull on you all the time. It also only pulls on your feet it doesn't pull directly on your internal organs so you would still be left with that oogy weightless feeling, you just wouldn't float around.
- Astronauts could attach themselves down with bungee cords (big elastic bands). They currently do this to exercise their muscles so that don't become too weak from lack of use. Unfortunately, you would have to disconnect them and reconnect them somewhere else as you tried to move around. It can be enough force to fool your feet but your internal organs would still feel weightless which leads to that oogy feeling.
- Magnets on your shoes and an iron floor would act similarly to the Velcro only it wouldn't make that cool ripping noise.
The only way to create a nearly realistic feeling of weight would be to create a spinning space station or shuttle.
The acceleration felt by the astronaut would be the centripetal acceleration which is
described by the formula The formula for this centripetal force would be This method would work well for simulating the force on the bottom of the feet but what about the forces on things that are not attached to the "floor" of the station. Would things not touching the floor (an apple, a baseball hat, or your internal organs) seem to have weight or not. If the your internal organs don't seem to have weight then we will have that oogy feeling we are trying to avoid. |
What happens if the astronaut drops the apple? Notice that when the apple is released, there is no longer a net force acting on it. So in the absence of a net force in continues on in the same direction and speed (constant velocity) that it had the instant it was released. From our point of view the apple moves in a straight line when released. From the astronaut's point of view (accelerated reference frame) the apple seems to drop in a straight line toward the floor. It seems to be pulled to the floor as if by gravity. The astronaut is fooled by what he sees into believing that there is gravity. The only time an oogy feeling comes over the astronaut is when he or she looks out the window and see the stars rolling around. It would be best to build this station with few windows... or make sure they are all covered with curtains. We have to make sure that we are not fooled into believing that somehow
centrifugal force is pushing the apple down or out away from the center. Centrifugal
force is a ghost force...it does not exist! |
If a station was created like the one at the left, while it is spinning,
the wall of the space station would apply a center seeking (centripetal) force on the
person to keep them traveling in a circular path. The wall of this station has to
exert that force (which also happens to be a 
The faster the space station
spins the greater the centripetal acceleration felt by the person. The larger the
radius of the space station the smaller the centripetal acceleration. By adjusting
the rotational velocity (v) of the space station we could literally adjust the
amount of the simulated gravity. If adjusted to just the right velocity, the
centripetal acceleration would equal the the acceleration due to gravity on Earth (ac
= g) which means we would be simulating the amount of gravity felt on Earth.
Any person in the space station would feel the same amount of force pushing on the bottom
of their feet as they would if they were standing on Earth.
The faster the
space station spins the greater the centripetal force needed to keep the person in a
circular path. The larger the radius of radius of the space station the smaller the
centripetal force. When ac = g then 
Consider the case of an apple held by the
astronaut. In order to be kept in a circular path, the astronaut will have to exert
a centripetal force on the bottom of the apple. This force will feel like the
"weight" of the apple. (true weight can only be caused by gravity) So the
astronaut will be fooled into thinking that the apple has weight. Since the apple is
an object not touching the floor and seems to have weight then we could say the internal
organs of the astronaut would also seem to have "weight." We wouldn't have
that oogy feeling.
This
is an image of a similar space station designed for simulating gravity. It
is from the film 2001: A Space Odyssey By Stanley Kubrik
�MGM
 |
This movie has some of the best and most realistic depictions of using centripetal force to simulate gravity. Click on either of the movie posters to see video clips that show this and other adaptations for working in space. |  |
